I have a small and growing stable of bikes and I notice on one in particular, a nearly 20 year old top-of-the-line steel frame from Bianchi, has a very different sensation riding. I'd call it decidedly flexy. Especially going over one of the local power climbs that are found all over New England, the short steep mounds you just muscle over, one can feel the frame giving, and moving. It's not a bad feeling at all! It feels lively, if I had to place an adjective to it.

Do stiffer frames really mean faster? Where is the science behind this? For the old salts who've ridden a variety of bikes across decades, can frames be too stiff?

I have seen a heatmap generated of a bicycle in use and there was no significant heat build-up between stiffer and less stiff frames indicating there should not be substantial energy loss associated with more compliance. Indeed, older builders even talked about avoiding making their frames too stiff. In searching for answers, I also came across riders (like Anquetil) using thinner tubing during TT efforts and thicker tubing during races that required sudden accelerations.

Depends on the quality of the asphalt you are riding on.For example a modern ultra stiff carbon frame with much inflated tires (120 psi+) will be a pain in the @@ while riding on very bad roads,your ride will be surely bumpy and slow and vice versa!

Faster isn't really a question of opinion. Its a statement of fact. Unfortunately, as best as I can tell, its a statement that isn't made with certainty either way.

Damon Rinard from Cervelo has stated that frames don't tend to show even within the range of error of (two) power meters (3%) if measuring at BB and hub. And so when one frame is say 20% stiffer than another, your gains would be 20% of something smaller than 3%. Unfortunately, he doesn't explicitly state what that less than 3% number is.

For the most part, stiffer will mean faster. There is a point of diminishing returns though. Ride quality needs to be taken into account which is why a frame should be rigid in the right places, but not overly rigid.

I rode the new Madone 6 series, and by god it felt like every watt was put directly to forward motion. A sensation I've never really felt. With that said though, the ride quality wasn't nearly as good as my Strong ti frame.

think you can have to stiff and you can have to flexy but anywhere in the middle is good and the middle covers quite a wide range.

stiffness has more to do with how it feels than how fast it is, stiff bikes are like 300psi in your tubs, feels real quite as your getting bounced all over the place but its really slow. To flexy and it wont go round a corner

Generally riders come in all shapes and sizes, everywhere from 55kg to 100kg is common, I meet both extremes on most Sunday rides. Some people easily generate a 1.700+ watt spike upon acceleration while others suffer to go above 1.000w.. So one mans stiff is another ones flexy. But in general, a stiffer frame will always feel more efficent in acceleration.

There is ofcourse a golden middle ground here, where efficency and comfort is in perfect harmony, but where that is depends on you as a rider.

Riding a track bike during winter as fixed training was great. Bikw was super stiff and had great position. Came to roads were slightly rough my tires were just chattering along which kn the other hand my roadie could glide over the same road with ease.

As said above, a stiffer bike feels different, but isn't inherently "faster".

The biggest actual difference I can come up with is how that feel translates to handling. That's like asking for suspension settings. Some prefer the handling a little looser and some want tight. Throw geometry, wheel choice, tire pressure and all the other variables into the mix and you can't boil a bike down to it's "stiffness" to determine how fast it is.

BTW, I am skeptical about claims that bikes "feel fast". One thing I like about Jan is he measures things, and his results in brevets (which aren't races, I understand) are impressive. I don't think we have the ability to accurately assess small changes in speed. It's like underpowered sports cars: they go zoom-zoom and feel zippy but they might still get dumped by some guy's overbuilt F350 pickup.

I read Jan Heine's ideas on the subject and that was part of the inspiration for asking this question. I'm seriously considering seeking out a flexy bike to add to my stable. I'm a younger guy though and took up riding in the generations of super-stiff Al and into the CF marketing craze of stiff bikes. I haven't really experienced this older bikes that some guys fondly like to recall. I have always been skeptical. But there's something gentle about the flex that I like and I was curious as to whether it could honestly affect a race result. With that being said, at 135 lbs and ride a 54 cm typically, I'm not exactly the sort of rider who can massively flex out a frame. Perhaps it's just a lot of bikes are too stiff for my size and style and not that they are generally too stiff. I'm not most Americans I suppose. I'd hate to have a custom bike built up and hate it because it's what some call "a noodle."

The builder I went to when I wanted a "racy steel frame" called that "snap and sway". As in under hard effort you want the bike to feel rhythmic and go with you. To flex just the right way that sort of compliments your effort, but to be stiff otherwise.

"Laterally stiff but vertically compliant". Kidding.

I can't say I've noticed that sensation as much. I went from riding a mid aughts aluminum race frame (with the obligatory Reynolds Ouzo Pro fork that was de rigeur on such frames) to the steel frame with a brief ride or two on a BMC Road Machine. I can say this: the steel frame is not as stiff as the aluminum frame, but the BMC wasn't either. Both the steel frame and the BMC (which I didn't ride very much) had more "snap" when standing than the aluminum frame which was uncomprimisingly stiff. The old "push the BB with your foot trick" resulted in alum frame > BMC > steel.

Now compare my steel "race" frame (which is built from Columbus Spirit, which is a thin, light tubeset ala Jan Heine's experience in that linked article) to a Surly Pacer (which I've also ridden) and they feel very different. My custom frame fits better, of course, but the front end feels much stiffer. In fact I get more flex from the ENVE fork than from the frame. But there is that sort of snap feeling I can notice that I don't feel on a Surly (which sort of just feels mushy). That's the best I can do to describe it.

Regarding the OP, stiffer is not faster. If anything, I think current trends in the peloton have resulted in less stiff frames than they were churning out ten years ago or so when aluminum was still being raced and carbon was slowly taking over. My experience on a, arguably cheaper alu frame from that era, was that it was incredibly stiff, but it sort of fought against you and on anything less than smooth as hell road, it was uncomfortable. Aluminum still kicks ass in the velodrome for a reason. There the stiffness is unlikely to slow you down as you are really looking at one hard acceleration accompanied by one or two smaller ones (depending on the race) and the course is crazy smooth.

Even if you love carbon (I like good bikes of any frame material), Henry James' FAQ regarding using steel is interesting. Especially his information on ride quality.

Aluminum, as far as I recall, is not technically stiffer than Ti or steel or composite, it usually results in stiffer frames because it is so low in density that one can make big exotic shapes that don't weigh more. My father still has a Raleigh Technicum (bonded aluminum... google it) frame from 86 or so that has fairly small diameter tubes (not even mildly oversized like a keirin frame or a boutique road job) and rode very similar to steel. The materials all have different characteristics regarding other properties (shock absorption, metal fatigue, etc) but I have been told that stiffness isn't really one of them. That more comes from what you make with it (size of tubes, shape, density of the weave, etc).

The fastest bike? The one you beat your old times on. That's one good use for Strava, haha.

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